This invention relates in general to gripping devices for transferring articles and in particular to a new and useful gripping device for handling stacks of flexible objects such as magazines.
When handling stacks of magazines formed at the discharge end of printing presses difficulties develop inasmuch as the printing inks are, in part, still wet and can, therefore, smear. If it is intended to put stacks of freshly printed magazines from the printing press on a pallet with a continuous bearing surface and possibly deposit them in multiple layers, no devices can be used in which the stacks are supported by a continuous or interrupted, such as forkshaped, carrying plate because the carrying plate would have to be pulled out from under the stack in a horizontal direction at the pallet storage location. The still wet printing ink on the bottom page of the lowermost magazine would be smeared, at least in part, in this process. Moreover, individual pages could be pulled along by adhering to the carrying plate and thus become creased.
Known from DE-OS No. 24 49 674 is a device for gripping stacks of flat objects, in which the stacks are held on two opposite side surfaces by means of two clamping jaws which are movable towards each other. But this gripping principle is suitable only for firm, unbending objects such as tiles. Flexible objects such as magazines would sag downwardly due to their weight and slip out of the gripping device.
The technical problem underlying the invention is to provide a device for handling stacks of flexible objects such as magazines or single sheets, by means of which the stacks can be gripped securely and all objects comprising the stack are treated gently.
In accordance with the invention, a device for gripping a stack of flexible articles such as magazines comprises a bearing plate for receiving the stack of articles with deflecting means associated therewith for deflecting the center of the articles upwardly and into an arched position relative to each end. A gripping mechanism is associated with the bearing plate and includes gripping arms which are movable toward and away from their respective ends of the stacked articles. Each arm contains a holding finger which may be pivotal to a horizontal position to engage beneath each end of the articles for lifting them off the bearing plate or which may be moved to a vertical position for releasing the articles. Gripping arms are advantageously moved by a fluid pressure operated device to move them into engagement or out of engagement with the stack of articles and the holding fingers are advantageously moved by a separately control device which also may be fluid pressure operated.
The stack lying on the bearing plate is pre-arched upwardly by the stack forming element. When the stack is subsequently gripped by the gripping mechanism in that the clamping jaws move toward each other, the stack is compressed laterally and thereby arched even more in the direction predetermined by the pre-arching operation. This imparts to the individual objects of the stack such an ample stiffness as not to be able to bend through downwardly and fall out of the gripping device. In their working position, the holding fingers disposed at the lower end of the clamping jaws support the two lower edge areas of the stack, thereby forming an additional safety against the stack falling out of the gripping mechanism. They are particularly expedient whenever the stack is subjected to high vertical acceleration or deceleration forces when being moved from the bearing plate to a remote pallet.
Since the stack need be supported additionally in a vertical direction in its lower edge area only because of being arched and because of its inherent stiffness caused thereby, the holding fingers may be comparatively short. This limits the contact area between holding fingers and stack underside to a minimum from the start. Shortness of the holding fingers brings yet another advantage, namely that the gripping mechanism may assume a relatively low position over the pallet when depositing the stack so that the stacks are dropped only a short distance when released.
According to another feature of the invention the stack forming element is formed by a bar which can be raised beyond the top of the bearing plate. The bar, preferably disposed in a central slot in the bearing plate, is retracted so far in its rest position that its top is flush with the top of the bearing plate. The bar is raised only when the stack is completely formed.
If no flat bearing surface is required for the formation of the stack, the stack forming element may be formed by the arched top of the bearing plate so that the individual objects of the stack are pre-arched already when placed on the bearing plate or stack.
In another development of the invention, the holding fingers are pivotable about a horizontal axis and in their rest position are flush with the clamping surface of the clamping jaws. Therefore, since the holding fingers are not retracted in a horizontal plane, but swung outwardly and, hence, downwardly, there is no danger that the possibly still wet printing ink of freshly printed magazines becomes smeared on the bottom side of the lowermost magazine and/or that individual pages are partly pulled along and are creased in the process. Due to the fact that the holding fingers are flush in their rest position with the clamping surface of the clamping jaws, the clamping surface of each clamping jaw forms a selfcontained, flat surface without protrusions and depressions. This eliminates the danger of individual magazines or sheets adhering to the clamping jaws when picking up or depositing a stack.
Advantageous features of the gripping mechanism are described in additional subclaims, one special advantage consisting in that the gripping mechanism is adjustable to accommodate stacks of different widths.
Due to the measure of mounting the transmission elements serving to drive the holding fingers in recesses in the clamping jaws, no additional space is needed for the accommodation of these transmission elements, which would otherwise either decrease the usable space between the clamping jaws or enlarge the outside dimensions and, hence, the space requirement of the gripping mechanism. The compact design permits depositing the stacks with comparatively narrow gaps.
Accordingly, it is an object of the invention to provide an improved device for lifting flexible articles which includes means for positioning the articles in an arched position so that a stack of the articles become reinforced so that the ends may be subsequently engaged by a gripping mechanism and lifted upwardly.
A further object of the invention is to provide a gripping device which includes gripping arms which are movable toward and away from articles which are arranged in an arched stack or deflected into an arched stack and which includes engagement fingers which are pivotal and which may be moved to horizontal positions so as to engage in recesses of the bearing plate on which the articles are stacked and lift them upwardly.
A further object of the invention is to provide a gripping device for engaging flexible artices which is simple in design rugged in construction and economical to manufacture.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.